Crude oil is known to contain a variety of metals, such as, alkali, alkaline earth metals, first transition metals, as well as Al, Sn, Pb, Sb, and the like. The presence of metals in crude oil during subsequent processing may cause corrosion, environmental pollution, and may poison the catalysts used. The metals may also interfere in oil refining processes by causing excessive coke formation.
Crude oil is conventionally fractionated in a crude distillation zone to produce several hydrocarbon fractions, such as naphtha, diesel, vacuum gas oil, and resid. The metals in the crude tend to concentrate in the heavier hydrocarbon fractions, and these heavier fractions including resid and gas oils are normally treated to reduce the metal content. For example, metals may be further concentrated in heavy bottoms or coke product in thermal processes such as coking and visbreaking. Metals may also be removed by adsorption onto solid particles such as catalysts or adsorbents. Such particles may be used in conjunction with hydrotreating processes that also reduce the nitrogen and sulfur content of the heavier hydrocarbon fractions.
PCT application PCT/GB2007/001985 published as WO 2007/138307 A2 discloses a sulfur-containing acid removal process for deacidifying a crude oil and/or crude oil distillate containing sulfur-containing acids comprising the steps of: (a) contacting the crude oil and/or crude oil distillate containing sulfur-containing acids with a basic ionic liquid having a melting point of below 150° C., and extracting at least a portion of the sulfur-containing acids into the basic ionic liquid as an extract phase; and (b) separating a crude oil and/or crude oil distillate phase which is reduced in acidity from the basic ionic liquid phase.
Liquid/Liquid Extraction of Metal Ions in Room Temperature Ionic Liquids, by Visser, Ann E., et al, Separation Science and Technology, 36(5&6), 785-804, (2001), Marcel Dekker, Inc., discloses the use of room temperature ionic liquids, specifically, 1-alkyl-3-methylimidazolium hexafluorophosphate, to separate metal ions from aqueous solutions.
U.S. Pat. No. 4,992,210 discloses a composition and method for improving the removal of corrosive contaminants from crude oil within the desalter in a petroleum refinery. An amine is added to the wash water or to the crude oil prior to processing in the desalter. The amine maximizes the yield of wash water removed from the desalter and substantially improves the removal of metal generating corrosive elements. The addition of the amine upstream of the desalter results in the removal of a significant amount of corrosive chlorides from the crude oil before it is passed through the fractionating unit and other refinery operations. The avoidance of adding metals and the assistance in removing other metals from the crude system aids in the reduction or elimination of downstream fouling and petroleum catalyst poisoning.
There remains a need in the art for improved processes that reduce the metal content of crude oil.